For reducing the component size of the electronic device, semiconductors have become the main components for the processors and controller in the electronic devices so as to reduce the size of the electronic devices and the functions of the devices are promoted greatly. However, these kinds of components are weak in the preventing of surge waves generated in the circuit. Thus it is important to prevent the destroy from surge waves in the electronic devices. Generally, there are two conditions which will induce surges in the circuit. One is switching surges due to the switching of the electric power switching. The other is from the nature phenomenon, such as lighting surges due to the thunderbolt to buildings. However all these surges will affect the operation of the electric device indoors, even the device will be destroyed or induce fire accident.
Generally, in electric devices or power system, fuse or fuseless switch are used as short circuit protection for transient high voltage or overload. However the reaction times of generally electric elements are about 2 ms, while the reaction time of the surge is several micro seconds (μs) which are very shorter than the transient reaction time of the electric elements. Thus, the fuse or fuseless switch is not enough for preventing the destroy from surges.
The prior art principle for the surge discharging device is by using a kernel element, varistor. The resistance of the varistor is changeable based on the voltage difference between two ends of the elements. The technologies are disclosed in Taiwan Patent No. M297037. Besides, in Taiwan Patent Publication No. 200623573, at lease one semiconductor field emission over-voltage protection device is disclosed. A semiconductor field emission over-voltage protection device is forwardly connected in parallel or forwardly connected with anti-parity. The protection device is also coupled to a front end of an I/O of a high frequency circuit, or is connected between an input end and a ground end. Above mentioned applications used in the normal voltage. The resistance of the varistor is very high. When the voltage has achieved to a predetermined value, the resistance will decrease rapidly with a react time of about several nano-second (ns). Thus, when a varistor is used to a surge discharging device, the surge discharging device is connected in parallel to a front end of an electric device. As a result, in normal operation voltage, the surge discharging device is used as in open circuit. When the voltage increases abnormally, it is used as in short circuit for prevent high energy from flowing into the electric device so that the surge has no effect to the electric device.